The percent abundance of the three stable isotopes of neon, Ne-20 (19.9924401754 amu), Ne-21 (20.99384668 amu), and Ne-22 (21.991385114 amu), are...

The percent abundance of the three stable isotopes of neon, Ne-20 (19.9924401754 amu), Ne-21 (20.99384668 amu), and Ne-22 (21.991385114 amu), are 90.5%, 0.3%, and 9.3%, respectively. Determine the average atomic mass of neon. (Report your answer to two places past the decimal point.)

please explain the sig fig on the answer.